Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, FIG. 1 depicts a conventional dual magnetic tunneling junction (MTJ) 10 as it may be used in a conventional STT-MRAM. The conventional dual MTJ 10 typically resides on a bottom contact 11, and includes a conventional bottom pinned layer 12, a conventional bottom tunneling barrier layer 14, a free layer 16, a conventional top tunneling barrier layer 18, and a conventional top pinned layer 20. Also shown is top contact 22. Conventional contacts 11 and 22 are used in driving the current in a current-perpendicular-to-plane (CPP) direction, or along the z-axis as shown in FIG. 1.
The conventional pinned layers 12 and 20 and the conventional free layer 16 are magnetic. The magnetic moments 13 and 21 of the conventional pinned layers 12 and 20, respectively are fixed, or pinned. In some conventional MTJs, this is accomplished by an exchange-bias interaction with AFM layers (not shown in FIG. 1). The conventional dual MTJ 10 is shown with the magnetic moments 13 and 21 in the dual state (antiparallel). In other cases, the magnetic moments 13 and 21 may be in the antidual state (parallel).
The conventional free layer 16 has a changeable magnetization 17. To switch the magnetization 17 of the conventional free layer 16, a current is driven perpendicular to plane (in the z-direction). When a sufficient current is driven from the top contact 22 to the bottom contact 11, the magnetic moment 17 of the conventional free layer 16 may switch to be parallel to the magnetic moment 13 of the conventional pinned layer 12. When a sufficient current is driven from the bottom contact 11 to the top contact 22, the magnetization 17 of the free layer may switch to be antiparallel to that of the pinned layer 12. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the conventional MTJ 10. In the dual state shown in FIG. 1, the conventional dual magnetic junction 10 may be switched at a lower current than for a conventional single MTJ or a dual MTJ in the antidual state.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. For example, mechanisms for improving the performance of STT-MRAM are desired. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories. The method and system described herein address such a need.